Osel scientists are actively pursuing a novel approach to block HIV transmission. This approach, termed MucoCept HIV, involves intravaginal administration of colonizing lactobacilli, the dominant bacteria normally lining the vaginal mucosa, which have been genetically modified to express HIV-binding proteins as a means of trapping and sequestering HIV particles at the mucosal surface. Subsequent exposure to Lactobacillus-produced substances, like lactic acid and hydrogen peroxide, is predicted to cause viral inactivation, thus reducing number of infectious particles reaching host cells and tissues. To date, specific accomplishments of the Osel team include the identification of natural vaginal colonizing strains of Lactobacillus, the determination of conditions for efficiently transforming these bacteria with foreign DNA and the expression of bioactive HIV-binding proteins, including two-domain CD4 (2D CD4). 2D CD4 has been expressed in both cell wall anchored and secreted formats. A key proof-of-concept was achieved with the demonstration that lactobacilli secreting 2D CD4 inhibit HIV-infectivity of susceptible cultured cells. Soluble 2D CD4 has been shown to exhibit a limited affinity for primary isolates of HIV. However, when imbedded within the biofilm matrix or anchored on the bacterial cell wall, .2D CD4 may be capable of a multivalent, high-avidity interaction with HIV particles. Nevertheless, to ensure that the most efficacious HIV ligand is developed for clinical studies, we propose to express additional CD4 variants, including oligomerized forms of the protein that have been shown by others to exhibit multivalent binding to HIV. Once an optimized CD4 protein has been chosen for development, we will then stably integrate its gene into the Lactobacillus chromosome and apply proprietary manufacturing and formulation technology to produce encapsulated MucoCept HIV product for subsequent safety, colonization, and efficacy studies in a primate model.